This invention relates to a method for application of a fluid to films and web materials which provides high speed multi-dimensional discrete registered placement of chemistry to enhance chemical functionality, appearance and structural integrity. The result of this method is material and consumer products with anisotropic chemical and physical properties in three dimensions. This method is particularly suitable for producing materials comprising gradients of such properties along any of the three dimensions. The method of this invention is particularly advantageous when used in connection with materials used in the production of personal care articles such as diapers, incontinence garments, training pants, feminine hygiene products such as sanitary pads and panty liners, and medical garments such as surgical gowns as it enables the deposition of chemical treatments at locations in the articles most beneficial to the use of the article. For example, in a diaper, it may be more beneficial to concentrate a chemical treatment for enhancement of fluid distribution only at the primary point of insult rather than have the chemical treatment located in places in which it may not be necessary.
Current methods for applying chemical treatments to substrate materials such as films and material webs often involve little control over the placement of the chemical treatments on or within the substrate materials. These methods include coating, spraying and dipping which do not permit placement of chemicals on such substrates with three-dimensional control over concentration of chemicals in substrates. Traditional spray technologies are relatively inefficient in placement of chemicals on the substrates, each droplet cannot be individually controlled for discrete placement, and only the directly exposed parts of the substrate are covered. U.S. Pat. No. 5,869,172 teaches a process for treating a porous substrate such as a fabric to produce internally coated porous materials in which a curable thixotropic material and one or more modifying materials are applied to the porous substrate as an impregnant. Sufficient energy is directed to the impregnant and porous substrate to cause the impregnant to flow into the porous substrate and force the modifier to specific positions within the substrate.
Printing techniques for application of inks to films and material webs are known; however, these techniques are typically limited to placement of the inks only on the surfaces of such substrates and do not permit placement of chemicals within the interior of the substrates, much less with three-dimensional control over chemical concentrations within the substrate. Such printing techniques include inkjet printers which employ computer controlled electrostatic charges for deposit of inks with a high degree of accuracy. See, however, International Publication No. WO 98/09798 which teaches a three dimensional printing materials system and method of use which includes building cross-sectional portions of a three-dimensional article and assembling the individual cross-sectional areas in a layer-wise fashion to form a final article. The individual cross-sectional areas are built by using an ink-jet printhead to deliver an aqueous solvent to an adhesive particulate mixture, causing the particles of the mixture to adhere together and to the previous cross-sectional areas.
Various webs and films have been electrically charged to enhance one or more properties of the web or film being treated. This includes the electrostatic treatment of various webs and films to enhance properties such as wettability, printability, adhesion and static reduction among others. Generally speaking, such treatments are achieved by directing a web or film which is to be electrically charged between a coupled pair of conducting bodies. One of the conducting bodies, if desired, may serve to direct the web or film through the charging apparatus. The other conducting body operates to develop a potential difference such that ionization and corona occurs. In this way, an electrostatic discharge is created between the conducting bodies, through which the web can pass to receive the desired treatment. U.S. Pat. No. 5,766,425 teaches a method for modifying the surface of a substrate to be treated in which an electrode structure causes an electric field/current to pass generally horizontally across the surface of the electrode structure and the substrate to be treated is positioned adjacent to the surface of the electrode structure, in turn, causing the discharge to flow horizontally across the substrate, thereby modifying the surface of the substrate so as to achieve an improvement in the desired properties.
Other methods employing electrostatic systems for applying materials to a substrate are taught, for example, by U.S. Pat. No. 4,748,043 in which an electrostatic coating system for applying a very thin coating to a substrate in air at atmospheric pressure comprises a plurality of spaced capillary needles disposed concentrically within the holes of an extractor plate, positioned in at least two rows and fed with coating liquid through a manifold, and a potential is developed between the capillary needles and the extractor plate affording a reduction of the liquid to a mist of highly charged droplets drawn to the substrate by a second electrical field; by related U.S. Pat. No. 5,552,012 and 5,585,170 which teach a method of using an electric field for contacting a substantially neutrally charged material, that is responsive to an electric field, with a substrate; and U.S. Pat. No. 5,807,437 which teaches a three-dimensional printing technique using a layered process in which a continuous-jet inkjet printer is used to deliver a binder to a bed of porous materials.
U.S. Pat. No. 4,859,266 teaches a method and apparatus for powder sewing two plies of cloth or fabric material by spraying an adhesive powder onto one side of one ply of cloth or fabric from a powder spray gun having a corona discharge electrode mounted thereon. A second pin electrode is provided on the opposite side of the one ply of cloth or fabric. Electrical charges of differing polarity are applied to the electrodes while the cloth or fabric is moved between them and the powder is sprayed thereon. In the course of migrating through the electrostatic field created between the two electrodes, the powder is caused to follow the force lines created within that field and to migrate onto one side of fabric in the form of a long, narrow band of powder. A second ply of cloth or fabric is placed over the first ply and the band of powder at which point pressure and heat are applied, activating the powder and causing it to become tacky, where, upon cooling, the two plies adhere together.
In contrast to known methods whereby powder (solid) materials can be made to migrate from one side of a porous substrate to the opposite side by application of an electrostatic field on both sides of the substrate material, the chemical treatments of interest in personal care absorbent articles are frequently fluids (liquids). It will be apparent to those skilled in the art that control of fluid distribution within a porous substrate is substantially different from the control of powder distribution within a porous substrate as taught by the prior art due to the differences in the physical properties of solids and liquids.
It is one object of this invention to provide a method for producing a material such as a fabric, textile, nonwoven or film having a gradient of at least one desired physical/chemical property, which gradient may extend in any one of an X, Y, or Z-direction of the material. As used herein, the X-direction and the Y-direction correspond to the directions of two perpendicular lines disposed in the same plane, and the Z-direction corresponds to the direction of a line perpendicular to the plane of the X- and Y-directions.
It is another object of this invention to provide a method for placement of fluids on and within substrates by which placement of each droplet of fluid can be individually controlled.
It is yet another object of this invention to provide materials suitable for use in personal care absorbent articles having chemical gradients extending in at least one of an X, Y and Z-direction.
It is yet another object of this invention to provide a method for placement of fluids on and within substrates which produces greater accuracy than conventional technologies.
It is a further object of this invention to provide a method for placement of fluids on and within substrates which is generally faster, more efficient and more reliable than conventional technologies.
These and other objects of this invention are addressed by a method for application of a fluid on a substrate formed as a film or web comprising the steps of locating the substrate between two spaced apart means for generating an electrostatic field, generating an electrostatic field on each side of the substrate, introducing a fluid as droplets for application to the substrate into the electrostatic field on at least one side of the substrate, thereby forming electrostatically charged droplets, and directing the electrostatically charged droplets based upon a predetermined pattern onto the at least one side of the substrate. The direction of the electrostatically charged droplets is preferably controlled by a computer generated signal. By appropriate control of the electrostatically charged droplets, the fluid may be caused to migrate from one side of the substrate into an interior portion of the substrate, i.e in the Z-direction. Similarly, the fluid may also be caused to migrate in the X- and Y-directions. In addition, by controlling the migration of the fluid within the substrate, fluid density gradients within the material may be generated.